The filtering systems of the type which we are concerned here are used to filter the liquid circulating in closed loop systems, such as swimming pools, dry cleaning tanks and the like. In such a system, a liquid is pumped through a particulate filter medium such as a filter-aid powder supported in layers on perforate support structures contained in a tank or housing. The liquid is forced under pressure into the housing and through the layers of powder to trap dirt and other particles on the surfaces of those layers. Such pressurized filters which use a powder as the filter medium are able to trap particles as small as 5 to 10 microns, as opposed to conventional sand or paper filters which are only able to remove particulate matter down to 50 to 100 microns.
In most prior systems of this general type, a pump in circuit with the liquid source, e.g., a swimming pool, circulates the liquid through the layers of filter-aid powder and their supports back to the liquid source. To save energy, this pump may be cycled on and off by a suitable timer. Initially, the supports or substrates, which are usually fabric covered perforate structures such as tubes, are loaded with the filter-aid powder by introducing the powder into the liquid stream upstream from the pump. The powder, entrained in the liquid, is trapped by the supports, providing even powder coatings or layers over all of the support surface areas. Once the filter layers are formed, the filter-aid powder remains attached to the supports even when liquid flow through the filter system is stopped or cycled on and off.
During operation of the filter system, dirt particles in the liquid are trapped by the filter medium as the liquid is recirculated, accumulating at the surfaces of the filter layers. Over time, the accumulation of dirt, pollen and other particulate matter forms coatings on the surfaces of the filter layers which greatly increase the back pressure in the system, causing reduced liquid flow and a reduction in overall system efficiency. Usually, the person responsible for the system will become aware at some point that the system is not operating up to par either because of reduced fluid flow, higher system pressure or ineffective filtering action. To remedy this situation, the operator usually replaces the filter powder. This procedure involves reversing the flow of liquid through the filter. In other words, the liquid is caused to flow backwards through the filter support structures underneath the filter-aid powder so that the powder is washed from those structures and settles to the bottom of the filter housing where it is collected and removed from the housing. After the support structures are cleaned as just described, normal liquid flow is resumed and fresh filter powder is introduced into the liquid upstream from the pump to recoat the support structures.
In a typical filter system serving a swimming pool, for example, the system may be cleaned thusly and recharged with fresh filter-aid powder on a monthly basis. It is obvious, however, that the system runs at maximum efficiency only at the very beginning of that time period because with each day's operation, the layers of filter-aid powder become progressively coated with dirt thereby constantly lowering system efficiency.
It has been known for some time that the filter medium becomes blocked primarily by dirt coating the surfaces of the filter layers rather than by penetration of dirt into those layers. It has also been recognized that the effectiveness of the filter medium can be restored by shaking the powder from the filter support structures using a handle attached to those structures with the pump turned off and, then, with the pump turned on again, recoating the support structures with the same powder particles. The dirt which was formally concentrated at the surfaces of the filter layers becomes mixed with the filter powder and no longer reduces the flow of liquid through the filter to any great extent. With the system back pressure reduced and the liquid flow increased almost to that of a freshly charged filter, this procedure allows the operator to save the cost of new filter powder that was formerly required with every cleaning of the filter. Thus, the procedure effectively extends the life of the filter powder many times and increases the efficiency and effectiveness of the filter system because the filter medium can be rejuvenated as often as the operator thinks to do so.
However, those prior art systems with shakable filter elements are disadvantaged in that the filter medium starts to become clogged with dirt from the first day after the filter medium is extended or regenerated. That is, after each regeneration, the system efficiency progressively deteriorates until the operator notices the increased pressure and reduced flow of liquid in the system. In many cases, the operator will delay the regeneration procedure because of neglect or laziness. During this time, filter system may be running with poor efficiency.
Attempts have been made to automatically actuate the shaker handle that shakes the filter elements on a periodic basis using timed electromechanical devices. However, these devices tend to be relatively complicated such that their costs are prohibitive. Moreover, when such timed devices are used, the filter pump's timer and the shaker device's timer have to be carefully synchronized because damage can occur if the shaker is actuated with the filter pump running.